This study was designed to investigated the antitumor effect and change chemosensitivity of chitosan in 2 kinds of humen lung cancer cell lines(NCI-H522, NCI-H596). To evaluate the antitumor effect and synergistic effectof chomosensitivity, MTT assay was used in vitro. then anticancer drugs used were 챤-platin , ectoposide, and adrimycin. The results of this study were as follows; Chitosan shwoed in antitumor effect on both NCI-H522 and NCI-H596. The lung cancer viability percent for NCI-H522 and NCL-H596 showed at the lowest levels of 5.31 and 5.33% when the concentration of chitosan was 25mg/$mell$ media and the exposure time of chitosan was 72 hours. ID50 value of chitosan on both NCI-H522 and NCI-H596 showed at the lowest levels of 14.07, 11.68 mg/$mell$ media when the exposure time of chitosan was 72 hours. the synergistic effect of chomosensitivity was better in NCI-H596 than in NCI0H522 . When the synergistic effect of chomosensitivity was shown according to the kind of the anticancer drugs, in case of NCI-H522 , in the concentration of 100$mu extrm{g}$/$mell$, ectoposide showed the highest synergistic effect of chomosensitivity and then was adrimycin In case of NCI-H596, in the concentration of 100$mu extrm{g}$/$mell$,, the order of the synergistic effect of chomosensitivity was ectoposide>adrimycin>cis-platin and in the concentration of 10$mu extrm{g}$/$mell$, ectoposide>cis-platin >adrimycin. It is concluded that chitosan is an active antitumor agent and is increased chomosensitivity though there is difference according to the kind and the concentration of anticancer drugs. But to be sued to lung cancer theraphy, further studies on toxicity, the mechanism of action, animal experiment are wanted.